The present invention relates generally to microneedles, and more particularly to microneedles fabricated by micromachining techniques.
As is well known, needles are used to extract samples of substances from living tissue in order to analyze the substances for diagnostic purposes, or to deliver a drug or a medicine. The majority of needles in use today are macroneedles, which have a relatively large diameter as compared to a blood cell and are on the order of millimeters (mm). The large diameter of the macroneedle shaft has the disadvantage of possibly damaging biological tissue during penetration. Additionally, tissue penetration by the needle is often painful to the patient because of the relatively large needle diameter.
One type of spring-actuated macroneedle penetrates tissue and drops blood to a chemical detector for measurement. While this needle may be less painful to the patient because penetration is of a relatively short duration, the needle is still relatively large and may damage tissue. Additionally, neither of the above-mentioned macroneedles provide real-time blood analysis.
As an alternative to macroneedles, microneedles having a diameter on the order of micrometers have many applications. For instance, they may be used as precise injection/extraction needles in cell biology, as injection/extraction heads in a drug delivery system or microchemical factory, and as injection/extraction heads in microsurgery. It is also advantageous to have a smaller size needle because the reduced size decreases discomfort and pain to the patient. This has been demonstrated in research on electrical microprobes made of silicon for an IC-compatible multichannel neural-recording array. The research has demonstrated that silicon microprobes with cross-sections on the order of tens of micrometers can penetrate living tissue without causing significant trauma. (K. Najafi, K. D. Wise and T. Mochizuki, "A High-Yield IC-Compatible Multichannel Recording Array," IEEE Micro Trans. on Electron Devices, vol. ED-32, pp. 1206-1211, July 1985.)
Recently, microneedles have been used with an inner diameter of approximately 20 micrometers (.mu.m) (1 .mu.m=1 micron=10.sup.-6 m). These microneedles are formed by heating the end of a glass pipette and lengthening the end until the diameter is reduced to about 20 .mu.m. Most cells in an animal such as a human measure 10-20 micrometers in diameter. Thus, while these glass microneedles can be used to insert and withdraw fluids and gases from a single cell, it is difficult to control the size of the needle shaft during fabrication. Additionally, the resulting needle is not very strong and real-time blood analysis is not possible. Another disadvantage of glass pipette needles is that it is difficult to incorporate electronics with such needles.
In view of the foregoing, an object of the present invention is to provide a microneedle having controllable and relatively small dimensions, including shaft width, and a method for making the same.
Another object of the present invention is to provide a microneedle which permits real-time analysis of a fluid being sampled.
Yet another object of the present invention is to provide a microneedle which minimizes the amount of trauma to the tissue being penetrated.
Still another object of the present invention is to provide a microneedle which may be mass produced.
Yet still another object of the present invention is to provide a microneedle which is strong enough to reliably penetrate biological tissue.
A further object of the present invention is to provide a microneedle which may incorporate micropumps, microvalves and microdetectors.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the claims.